The stink that exists in your favorite couch cushion as a result of the 4,000 or so farts that you've pumped into it during its lifetime. Normally surfacing when you drop down fast on said cushion and release the yesterfarts back into your face.

You: "Thanks for dropping by. Why don't you have a seat and make yourself at home?"

Victim: "Sure thing. Well I wanted to talk to you about...holy shit, did you just cut one?"

You: "No"

Victim: "Yes you did!" Your ass smells like old potato chips and mayonnaise!"

You: "That wasn't me. I noticed you flopped onto my cushion so what you're smelling are my yesterfarts. Now can we get back to our conversation and you're inevitable question on whether or not I fucked your mother? Yes, by the way."